Malathion
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alberto Plate [2]
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Overview
Malathion is an organophosphate that is FDA approved for the treatment of pediculus humanus capitis (hair lice). Common adverse reactions include application site irritation, skin irritation.
Adult Indications and Dosage
FDA-Labeled Indications and Dosage (Adult)
Pediculus Humanus Capitis
- (1)Apply Malathion Lotion on dry hair in amount just sufficient to thoroughly wet the hair and scalp. Pay particular attention to the back of the head and neck while applying Malathion lotion. Wash hands after applying to scalp.
- (2)Allow hair to dry naturally - use no electric heat source, and allow hair to remain uncovered.
- (3)After 8 to 12 hours, the hair should be shampooed.
- (4)Rinse and use a fine - toothed (nit) comb to remove dead lice and eggs.
- (5)If lice are still present after 7 - 9 days, repeat with a second application of Malathion Lotion.
- (6)Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment.
Off-Label Use and Dosage (Adult)
Guideline-Supported Use
Infestation by Phthirus pubis
- Dosage: Malathion 0.5% lotion applied for 8 to 12 hours and washed off[1]
Non–Guideline-Supported Use
There is limited information regarding Off-Label Non–Guideline-Supported Use of Malathion in adult patients.
Pediatric Indications and Dosage
FDA-Labeled Indications and Dosage (Pediatric)
Pediculus Humanus Capitis
- (1)Apply Malathion Lotion on dry hair in amount just sufficient to thoroughly wet the hair and scalp. Pay particular attention to the back of the head and neck while applying Malathion lotion. Wash hands after applying to scalp.
- (2)Allow hair to dry naturally - use no electric heat source, and allow hair to remain uncovered.
- (3)After 8 to 12 hours, the hair should be shampooed.
- (4)Rinse and use a fine - toothed (nit) comb to remove dead lice and eggs.
- (5)If lice are still present after 7 - 9 days, repeat with a second application of Malathion Lotion.
- (6)Further treatment is generally not necessary. Other family members should be evaluated by a physician to determine if infested, and if so, receive treatment.
Off-Label Use and Dosage (Pediatric)
Guideline-Supported Use
There is limited information regarding Off-Label Guideline-Supported Use of Malathion in pediatric patients.
Non–Guideline-Supported Use
Scabies
- Dosage: 0.5% malathion lotion.
Contraindications
Malathion Lotion is contraindicated for neonates and infants because their scalps are more permeable and may have increased absorption of malathion. Malathion Lotion should also not be used on individuals known to be sensitive to malathion or any of the ingredients in the vehicle.
Warnings
- Malathion Lotion is flammable. The lotion and wet hair should not be exposed to open flames or electric heat sources, including hair dryers and electric curlers. Do not smoke while applying lotion or while hair is wet. Allow hair to dry naturally and to remain uncovered after application of Malathion Lotion.
- Malathion Lotion should only be used on children under the direct supervision of an adult.
- If Malathion Lotion comes into contact with the eyes, flush immediately with water. Consult a physician if eye irritation persists.
- If skin irritation occurs, discontinue use of product until irritation clears. Reapply the Malathion Lotion, and if irritation reoccurs, consult a physician.
- Slight stinging sensations may occur with the use of Malathion Lotion.
Adverse Reactions
Clinical Trials Experience
Dermatologic Effects
- Irritation of Skin and Scalp
Ophthalmologic Effects
Postmarketing Experience
There is limited information regarding Malathion Postmarketing Experience in the drug label.
Drug Interactions
There is limited information regarding Malathion Drug Interactions in the drug label.
Use in Specific Populations
Pregnancy
- There was no evidence of teratogenicity in studies in rats and rabbits at doses up to 900 mg/kg/day and 100 mg/kg/day malathion, respectively. A study in rats failed to show any gross fetal abnormalities attributable to feeding malathion up to 2,500 ppm (∼ 200 mg/kg/day) in the diet during a three-generation evaluation period.
- These doses were approximately 40 to 180 times higher than the dose anticipated in a 60 kg adult (based on body surface area and assuming 100% bioavailability). Because animal reproduction studies are not always predictive of human responses, this drug should be used (or handled) during pregnancy only if clearly needed.
Pregnancy Category (AUS):
There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Malathion in women who are pregnant.
Labor and Delivery
There is no FDA guidance on use of Malathion during labor and delivery.
Nursing Mothers
- Malathion in an acetone vehicle has been reported to be absorbed through human skin to the extent of 8% of the applied dose. However, percutaneous absorption from the Malathion Lotion, 0.5% formulation has not been studied, and it is not known whether malathion is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Malathion Lotion is administered to (or handled by) a nursing mother.
Pediatric Use
- The safety and effectiveness of Malathion Lotion in children less than 6 years of age has not been established via well-controlled trials.
Geriatic Use
There is no FDA guidance on the use of Malathion in geriatric settings.
Gender
There is no FDA guidance on the use of Malathion with respect to specific gender populations.
Race
There is no FDA guidance on the use of Malathion with respect to specific racial populations.
Renal Impairment
There is no FDA guidance on the use of Malathion in patients with renal impairment.
Hepatic Impairment
There is no FDA guidance on the use of Malathion in patients with hepatic impairment.
Females of Reproductive Potential and Males
There is no FDA guidance on the use of Malathion in women of reproductive potentials and males.
Immunocompromised Patients
There is no FDA guidance one the use of Malathion in patients who are immunocompromised.
Administration and Monitoring
Administration
- Lotion (Topic application)
Monitoring
- There are no special laboratory tests needed in order to use this medication.
IV Compatibility
There is limited information regarding the compatibility of Malathion and IV administrations.
Overdosage
- Consideration should be given, as part of the treatment program, to the high concentration of isopropyl alcohol in the vehicle. Malathion, although a weaker cholinesterase inhibitor than some other organophosphates, may be expected to exhibit the same symptoms of cholinesterase depletion after accidental ingestion orally. If accidentally swallowed, vomiting should be induced promptly or the stomach lavaged with 5% sodium bicarbonate solution. Severe respiratory distress is the major and most serious symptom of organophosphate poisoning requiring artificial respiration, and atropine may be needed to counteract the symptoms of cholinesterase depletion.
- Repeat analyses of serum and RBC cholinesterase may assist in establishing the diagnosis and formulating a long-range prognosis.
Pharmacology
Mechanism of Action
Malathion is an organophosphate agent which acts as a pediculicide by inhibiting cholinesterase activity in vivo.
Structure
- The chemical name of malathion is (±) - [(dimethoxyphosphinothioyl) - thio] butanedioic acid diethyl ester. Malathion has a molecular weight of 330.36, represented by C10H19O6PS2, and has the following chemical structure:
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Pharmacodynamics
There is limited information regarding Malathion Pharmacodynamics in the drug label.
Pharmacokinetics
There is limited information regarding Malathion Pharmacokinetics in the drug label.
Nonclinical Toxicology
There is limited information regarding Malathion Nonclinical Toxicology in the drug label.
Clinical Studies
- Two controlled clinical trials evaluated the pediculicidal activity of Malathion Lotion. Patients applied the lotion to the hair and scalp in quantities, up to a maximum of 2 fl. oz., sufficient to thoroughly wet the hair and scalp. The lotion was allowed to air dry and was shampooed with Prell shampoo 8 to 12 hours after application. Patients in both the Malathion Lotion group and in the vehicle group were examined immediately after shampooing, 24 hours after, and 7 days after for the presence of live lice. Results are shown in the following table:
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The presence or absence of ova at day 7 was not evaluated in these studies. The presence or absence of live lice or ova at 14 days following treatment was not evaluated in these studies. The residual amount of malathion on hair and scalp is unknown.
How Supplied
Malathion Lotion, USP 0.5%, is supplied in bottles of 2 fl. oz. (59 mL)
Storage
Store at controlled room temperature 20° to 25°C (68° to 77°F)
Images
Drug Images
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Package and Label Display Panel
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Patient Counseling Information
There is limited information regarding Malathion Patient Counseling Information in the drug label.
Precautions with Alcohol
Alcohol-Malathion interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.
Brand Names
Look-Alike Drug Names
There is limited information regarding Malathion Look-Alike Drug Names in the drug label.
Drug Shortage Status
Price
References
The contents of this FDA label are provided by the National Library of Medicine.